He says he used reasonable force.

The American police officer who shot deadAustralian woman Justine Damond Ruszczyk will plead not guilty to murder and manslaughter charges.

Mohamed Noor, 32, has tendered legal documents indicating he will argue that he used reasonable force acting in self-defence on the night of July 15, 2017.

Damond Ruszczyk, 40, died of a gunshot wound to the abdomen minutes after calling 911 to report a suspected sexual assault in an alleyway near her Minneapolis home.

The life coach was weeks away from getting married.

Last month prosecutors stated that Noor, who was in the passenger seat, shot Damond Ruszczyk when he was startled.

"There is no evidence Officer Noor encountered a threat, appreciated a threat, investigated a threat or confirmed a threat that justified his decision to use deadly force," said Hennepin County Attorney Mike Freeman.

"Instead Officer Noor recklessly and intentionally fired his handgun from the passenger seat in disregard for human life."

He's been charged with third-degree murder and second-degree manslaughter.

Third-degree murder carries a maximum 25 years behind bars, while the latter carries 10 years.

No police officer has ever been prosecuted over a fatal shooting in the state of Minnesota.